Thanks - that's helpful, but I don't see anything organic there. I think the brown lump is a weathered piece of ferruginous siltstone, probably concretionary in origin. The onion-skin layering is typical of that, though it may also have been enhanced by more recent weathering. As a whole, you have a lump of sandstone containing that lump (probably one of many in the original deposit). Sandstones do sometimes have larger clasts within them, ranging from just the occassional one, through quite a few, to conglomerate, where the clasts form the majority of the rock, with a relatively small amount of sandstone between.